Proof-Load Tables — UNC
Proof load is the tension a finished bolt must hold without permanent stretch. It is below yield and well below breaking load. This table gives proof loads for coarse-thread inch bolts.
Proof load, lbf (proof stress x tensile stress area)
| Size-TPI | Stress area (sq in) | Grade 2 | Grade 5 | Grade 8 |
|---|---|---|---|---|
| 1/4-20 | 0.0318 | 1,750 | 2,700 | 3,820 |
| 5/16-18 | 0.0524 | 2,880 | 4,460 | 6,290 |
| 3/8-16 | 0.0775 | 4,260 | 6,590 | 9,300 |
| 7/16-14 | 0.1063 | 5,850 | 9,040 | 12,760 |
| 1/2-13 | 0.1419 | 7,800 | 12,060 | 17,030 |
| 9/16-12 | 0.1819 | 10,010 | 15,470 | 21,830 |
| 5/8-11 | 0.2260 | 12,430 | 19,210 | 27,120 |
| 3/4-10 | 0.3345 | 18,400 | 28,430 | 40,140 |
| 7/8-9 | 0.4617 | 15,240 | 39,250 | 55,410 |
| 1-8 | 0.6057 | 19,990 | 51,490 | 72,690 |
| 1-1/8-7 | 0.7633 | 25,190 | 56,480 | 91,590 |
| 1-1/4-7 | 0.9691 | 31,980 | 71,710 | 116,290 |
| 1-3/8-6 | 1.1549 | 38,110 | 85,460 | 138,590 |
| 1-1/2-6 | 1.4053 | 46,370 | 103,990 | 168,630 |
Proof stress: Grade 2 = 55 ksi to 3/4 in, 33 ksi above; Grade 5 = 85 ksi to 1 in, 74 ksi above; Grade 8 = 120 ksi. Stress area per ASME B1.1. Rounded to 10 lbf.
These tables carry the same figures as the printed sheet below.
The printed sheet
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Text version of this sheet
SAE J429 proof loads · UNC coarse thread
What it is
FIELD IDENTIFICATION
Proof load is the tension a finished bolt must hold without permanent stretch. It is below yield and well
below breaking load. This table gives proof loads for coarse-thread inch bolts.
Proof load: the tension a bolt must hold
without permanent stretch
Proof load, lbf (proof stress x tensile stress area)
Size-TPI
Stress area (sq in)
Grade 2
Grade 5
Grade 8
1/4-20
0.0318
1,750
2,700
3,820
5/16-18
0.0524
2,880
4,460
6,290
3/8-16
0.0775
4,260
6,590
9,300
7/16-14
0.1063
5,850
9,040
12,760
1/2-13
0.1419
7,800
12,060
17,030
9/16-12
0.1819
10,010
15,470
21,830
5/8-11
0.2260
12,430
19,210
27,120
3/4-10
0.3345
18,400
28,430
40,140
7/8-9
0.4617
15,240
39,250
55,410
1-8
0.6057
19,990
51,490
72,690
1-1/8-7
0.7633
25,190
56,480
91,590
1-1/4-7
0.9691
31,980
71,710
116,290
1-3/8-6
1.1549
38,110
85,460
138,590
1-1/2-6
1.4053
46,370
103,990
168,630
Proof stress: Grade 2 = 55 ksi to 3/4 in, 33 ksi above; Grade 5 = 85 ksi to 1 in, 74 ksi above; Grade 8 = 120 ksi. Stress area per ASME B1.1. Rounded to 10 lbf.
Key points
Proof load is not a working load. Design loads are set by the engineer with a safety factor.
Governing standards: SAE J429 (2014); ASME B1.1-2023. Editions shown are the latest confirmed as of September 2026. The drawing and the governing standard always take
precedence over this sheet.
torquing any fastener. Verify the current governing standard, project documents, OEM requirements, size, thread, coating and lot certification. To the fullest extent permitted by law, The Fastener App disclaims liability
arising from reliance on this reference.
Fastener Guide reference FG-BD5343 · thefastenerapp.com/fastener-guide/technical-reference/proof-load-tables-unc · © The Fastener App. Reference only — verify the current governing standard, drawing and manufacturer data before specifying or installing.
